This invention relates to a method for the detection of authenticity in a data carrier by measuring the permeability in respect of an electromagnetic radiation, preferably infra-red radiation, of at least one region of the data carrier. The invention also relates to apparatus for carrying out said method.
German OS No. 26 35 795 describes a data carrier with a really distributed random information in the form of magnetic fibres. A lamellar scanning trace is used for identification. In order to ensure that this lamellar trace is adhered to with maximum accuracy lateral stops or a self-centering device for the magnetic head by means of corresponding markings on the data carrier are provided. German OS No. 28 29 778 describes a data carrier which is provided with a linear trace of a material having a property which distinguishes it from the adjacent regions of the data carrier to provide a basis for identification. In both of these arrangements the degree of reproduceability and thus the accuracy of the authenticity test of such a data carrier depend on how accurately the trace is scanned. Even such factors as variations in temperature or variations in the humidity content of the data carrier are liable to give rise to false readings. German OS No. 28 47 756 describes a method for testing authenticity which uses permeability to infrared radiation as a critical parameter.